1. Field of the Invention
The present invention relates to a metal catalyst carrier, particularly to such having a quasi-elliptical cross section and a resistance to thermal stress.
2. Description of the Related Art
Catalyst carriers, such as those carrying a catalyst for purifying automobile exhaust gas, must be lightweight and resistant to vibration impact. For such applications, a known metal honeycomb column is composed of flat and wavy sheets or foils, of a heat-resisting ferritic stainless steel, for example, laminated, wound together and bonded to each other.
This type of metal catalyst carrier, satisfying the above-mentioned properties, has an about ten times greater thermal expansion coefficient than that of ceramic catalyst carriers, so that thermal stress which occurs when the automobile engine stops may cause a failure at the bond between the flat and wavy sheets and/or at the bond between the metal honeycomb column and a columnar metal case fittingly enclosing the honeycomb column.
As a solution to this problem, Japanese Unexamined Patent Publication (Kokai) No. 2-273549 proposed a metal honeycomb column having a circular cross section, in which flat and wavy sheets are bonded at a smaller bond rate in the peripheral portion than in the core portion of the honeycomb column. The bond rate is defined as a number or quotient obtained by dividing a bonded area by a total area in which the laminated and wound flat and wavy sheets meet or are in contact with each other.
It is currently desired, however, that a catalyst carrier should be flat or have a quasi-elliptical cross section suitable for equipment in the limited underfloor space of automobiles. Such a quasi-elliptical cross section is subjected to a different distribution of thermally induced stress than a circular cross section. Moreover, a problem also arose in that the bond between the honeycomb column and the metal case enclosing the former is broken by thermally induced deformation of the catalyst carrier.